Get basic UI working and refactor transport modes

Bunch of stuff in this PR that I'd appreciate review on.

This was a bit rushed but I've done the following:

- Update Rails
- Update other gems
- Removed Angular from the manifest
- Refactored the transport modes into actual database models
- Got basic UI working with just some jQuery
- Setup puma for Heroku

You can test it out here: https://rerouteit.herokuapp.com/

I've still got to write the tests for the `TripService`.
Prefer double-quoted strings unless you need single quotes to avoid extra backslashes for escaping.